The rufous hummingbird (Selasphorus rufus) migrates as far as 3,900 miles (one way!) and requires nectar at every stop on its journey. While non-native thistles can be invasive, at least 13 species are native to Arizona and an important food source for pollinators. Photo Courtesy of Bruce Taubert.

Author: Alexandra (Lexi) Cegielski, ASU Undergraduate Student and Researcher

Lexi Cegielski is an undergraduate student at Arizona State University majoring in Sustainability and Urban Planning. She is passionate about creating sustainable cities and preserving wildlife. Growing up in Arizona, Lexi spends her free time enjoying the outdoors with friends and family. In her spare time, she loves baking vegan desserts, hiking, and practicing yoga. To learn more about Lexi’s work and passions, visit her LinkedIn. 

Did you know that residential yards cover roughly 30% of land in the United States? This is one reason why the Arizona Wildlife Federation seeks to expand gardening for wildlife in people’s yards and neighborhoods. This includes a certification program —led by the National Wildlife Federation — that promotes the provisioning of food, water, and shelter (i.e., wildlife habitat) in residential and other gardens. You may be wondering: can residents’ yards benefit wildlife and related conservation efforts? The short answer is yes — and scientific evidence has proven it. 

Researchers affiliated with Arizona State University and the U.S. Forest Service, among others, have evaluated vegetation and bird diversity in NWF-Certified Wildlife Habitat®. Focusing on residential yards, the research team compared biodiversity in certified habitats and different types of lawns and natural areas in six U.S. cities. Specifically, the team collected data on vegetation and bird species in metropolitan Phoenix, as well as Los Angeles, Miami, Baltimore, Boston, and Minneapolis–St. Paul.

Researchers collected data on vegetation and bird species in three types of residential yards and two types of natural areas, as shown in the graph to the right below. The yard types included NWF-certified habitat and two types of lawns (defined as yards covered by at least 75% turfgrass): those fertilized (called high-input lawns) and not fertilized (low-input lawns). For each yard type, several different residential properties were surveyed in each of the six metro regions.

The team also surveyed two types of parks as “reference sites.” The idea here was to compare vegetation and bird diversity in these relatively undeveloped areas that contain wildlife habitat. Interstitial parks were sites within the metropolitan region that are managed as parks compared to relatively unmanaged nature preserves (i.e., representing native ecosystems such as the Sonoran Desert in Phoenix). For each type of reference site, 4 or 5 parks were evaluated from each metro region for a total of more than 25 natural sites.

So, what did the biodiversity surveys entail? Imagine going into your own yard and counting all of the different types of plants and birds you see. How many different species would you see? This approach essentially mirrors the methodology the researchers used to assess the diversity of species across different landscape types. This method of field research is known as community ecology surveys, and the goal is to document every unique species of bird and vegetation. In inventorying vegetation, the researchers documented cultivated vegetation including purposely planted trees, shrubs, and herbaceous (non-woody) plants. The team also inventoried “weeds”, which they consider “spontaneous vegetation” (i.e., since they are not intentionally cultivated). The field surveys generated various measures of biodiversity, including species richness — which is the number of different species of vegetation or birds found at each site. The researchers then compared species richness across the different types of yards and reference sites.

Plant Diversity

Plant ecologist Dr. Josep Padullés Cubino, who formerly was affiliated with the University of Minnesota but now is a professor at the Autonomous University of Barcelona, led the assessment of vegetation diversity. Dr. Padullés Cubino discovered that NWF-certified gardens hosted the highest total number of vegetation at 1,408 species, followed by low-input lawns, then high-input lawns, and reference natural areas. While we might expect higher plant variety in natural areas versus yards, the opposite was found to be true. The higher species richness per unit area in residential yards compared to natural areas is due to the introduction and maintenance of non-native species found at nurseries.

A graphic related to vegetation diversity is known as a species accumulation curve (below right), which shows the differences in the number of species between each landscape type. From the figure, we clearly see that NWF-certified gardens host a larger number of species than other landscape types, including both types of lawns and the two reference sites. In fact, notice how the top line is still on an upward trend at 25 sampled plots. This indicates that even more species would have been found if the team continued to collect data from additional gardens.  

Certified wildlife yards also excelled compared to various-input lawns because of the higher variation inseed mass. Higher seed mass essentially means more food sources for birds and other wildlife available. Additionally, seed mass increases the ability of plants to reproduce. In all, plant diversity in a garden is crucial for wildlife to feast and live. 

Ensuring your wildlife garden contains various plants is an exceptional start to a successful wildlife garden. From the words of the expert himself, Josep Padullés Cubino reminds you that, “Wildlife gardening is a process that takes time. Be patient and take time to observe the changes in your garden and the wildlife it attracts.”

Bird Diversity

Wildlife ecologist Dr. Susannah Lerman, who is a Research Ecologist with the U.S. Forest Service, is passionate about native birds. In a publication she led with Dr. Desiree Narango, the team demonstrated that residential yards — regardless of the type — supported a greater number of bird species compared to the reference natural areas (i.e., parks). Unlike vegetation diversity, yards with NWF-certified habitats hosted similarly high species richness in the bird communities as the low- and high-input lawns. Yet community turnover — another measure of biodiversity — was uniquely highest in wildlife-certified yards compared to other yard types. Community turnover evaluates the magnitude of changes in the species present from one yard to another. What this essentially means is that in high-input lawns, we are likely to find the same common species — for example, rock pigeons, house sparrows, and great-tailed grackles — from one lawn to the next. But in NWF-certified yards, we see more changes in bird species from one NWF-certified yard to another. For instance, in one certified yard, you might see an Abert’s towhee, Anna’s hummingbird, and verdin, yet in the next, you might also see cactus wren, and in the next a curve-billed thrasher, and yet in another, a greater roadrunner. The image below, designed by Dr. Lerman, demonstrates the idea of community turnover with bird species common in the U.S. While lawn after lawn we see pigeons, sparrows, and grackles, the species in certified yards vary more greatly from habitat to habitat (i.e., a robin, cardinal, and woodpecker may be in one certified habitat yard, but in the next we see a robin along with wood thrush and chickadee, and in additional residential habitats we pick up additional species such as a grey catbird and yellow warbler. 

Dr. Lerman and colleagues’ research also found that neighborhoods withabundant tree canopy feature more diverse birds, and especially in warmer regions such as Arizona, trees can be a great way for species to stay cool and protected from threats. Meanwhile, impervious surfaces can exacerbate heat and lower biodiversity. Thus, in addition to managing yards as a wildlife habitat by following NWF’s certification guidelines, additional tips for attracting birds include increasing tree cover and reducing impervious surfaces such as patios. 

Lerman’s team also found that residential wildlife habitats tend to attract bird species with “high public interest,” or in other words, birds that people tend to appreciate and enjoy seeing. Example species include the Gilded Flicker and Costa’s Hummingbird. In contrast, the natural areas, or parks, tend to support “species of conservation concern,” which are birds that are imperiled due to declines in their populations. Example species of concern are the Cactus Wren and Gambel’s Quail. As a result, Dr. Lerman and colleagues advocate for both “land sparing” and “land sharing” approaches to conservation; while land sparing involves protecting natural areas in parks and preserves, land sharing entails residents creating wildlife habitat to share their yards with wildlife. Through both land sparing and sharing, human-dominated landscapes such as cities can protect wildlife and help preserve biodiversity.

Final Thoughts

In sum, scientific evidence from field research confirms that NWF-certified habitats in people’s yards enhance conservation by hosting diverse vegetation, which in turn supports varied bird species that people appreciate. Thus, residents can directly make a difference in their own yards by managing bird habitats. Not only does wildlife gardening provide shelter and resources for diverse wildlife, but people also reap related benefits. As Dr. Lerman notes, “There's also a lot of joy that comes from seeing different kinds of birds in your backyard.” 

To find out how to get certified or otherwise garden for wildlife, visit www.nwf.org/CERTIFY

Learn more about certified wildlife gardens in Arizona

Get tips on how to make your wildlife garden beautiful and low-maintenance

Be sure to sign up for Arizona Wildlife Federation’s E-News to receive regular updates on Gardening for Wildlife in Arizona!

Meet the ASU Team

Sources 

Lerman, S. B., Narango, D. L., Avolio, M. L., Bratt, A. R., Engebretson, J. M., Groffman, P. M., Hall, S. J., Heffernan, J. B., Hobbie, S. E., Larson, K. L., Locke, D. H., Neill, C., Nelson, K. C., Padullés Cubino, J., & Trammell, T. L. E. (2021). Residential yard management and landscape cover affect urban bird community diversity across the continental USA. Ecological Applications, 31(8), e02455. https://doi.org/10.1002/eap.2455

Lerman, S.B., K.L. Larson, D.L. Narango, M.A. Goddard, and P.P. Marra. 2023. Humanity for habitat: Residential yards as an opportunity for biodiversity conservation. Bioscience. 73: 671-689. https://doi.org/10.1093/biosci/biad085

Padullés Cubino, J., Cavender-Bares, J., Groffman, P. M., Avolio, M. L., Bratt, A. R., Hall, S. J., Larson, K. L., Lerman, S. B., Narango, D. L., Neill, C., Trammell, T. L. E., Wheeler, M. M., & Hobbie, S. E. (2020). Taxonomic, phylogenetic, and functional composition and homogenization of residential yard vegetation with contrasting management. Landscape and Urban Planning, 202, 103877. https://doi.org/10.1016/j.landurbplan.2020.103877

Note: the species accumulation curve above was Figure 2 published by Elsevier in https://www.sciencedirect.com/science/article/abs/pii/S0169204620300323?via%3Dihub